1. Field of the Invention
The present invention relates to a spiral wound gasket, and more particularly relates to a spiral wound gasket with improved sealability at pipe joints.
2. Description of the Related Art
Spiral wound gaskets are known in which a hoop member made of metal and formed into a V- or W-shape in cross section and a filler member made of inorganic paper mainly composed of rock wool, ceramic fiber, or the like are laid one on top of the other and wound together (see Japanese Examined Utility Model Publication No. H6-000693 and Japanese Laid-Open Patent Publication No. H10-141503, for example). Such spiral wound gaskets are used as sealing materials for achieving airtightness or liquid-tightness at joints of various types of piping.
For example, exhaust pipe joints for automobiles are manufactured through pressing or casting. However, especially when pressing is employed, sufficient dimensional accuracy cannot generally be achieved with press-formed products, or welding distortion may be caused during welding between a flange portion and a pipe portion. In a state in which such insufficient dimensional accuracy or distortion is present, even if a spiral wound gasket is disposed between flanges at joints, it is difficult to ensure uniform sealability.
Moreover, such flanges are likely to bend due to a fastening axial force of bolts, and it is therefore difficult to maintain a constant compression amount in the circumferential direction of a gasket. Also, in connection with recent reduction in fuel consumption of vehicles, there is a trend toward reduction of the plate thickness of a flange itself and the number of bolting positions so as to achieve weight and cost reduction. Thus, there is concern that bending of flanges will increase even more.
Therefore, there is demand for development of a spiral wound gasket that is capable of filling (hereinafter also referred to as “conforming to”) a possible flange gap when compressed and thereby exhibiting sufficient sealability and that has even more improved conformability (i.e., that can allow for a large compression amount).